 |
| Titel |
Seasonal and elevational variations of black carbon and dust in snow and ice in the Solu-Khumbu, Nepal and estimated radiative forcings |
| VerfasserIn |
S. Kaspari, T. H. Painter, M. Gysel, S. M. Skiles, M. Schwikowski |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 15 ; Nr. 14, no. 15 (2014-08-13), S.8089-8103 |
| Datensatznummer |
250118942
|
| Publikation (Nr.) |
 copernicus.org/acp-14-8089-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
| Black carbon (BC) and dust deposited on snow and glacier surfaces can reduce
the surface albedo, accelerate snow and ice melt, and trigger albedo
feedback. Assessing BC and dust concentrations in snow and ice in the
Himalaya is of interest because this region borders large BC and dust
sources, and seasonal snow and glacier ice in this region are an important
source of water resources. Snow and ice samples were collected from crevasse
profiles and snow pits at elevations between 5400 and 6400 m a.s.l. from Mera
glacier located in the Solu-Khumbu region of Nepal during spring and fall
2009, providing the first observational data of BC concentrations in snow
and ice from the southern slope of the Himalaya. The samples were measured
for Fe concentrations (used as a dust proxy) via ICP-MS, total impurity
content gravimetrically, and BC concentrations using a Single Particle Soot
Photometer (SP2). Measured BC concentrations underestimate actual BC
concentrations due to changes to the sample during storage and loss of BC
particles in the ultrasonic nebulizer; thus, we correct for the
underestimated BC mass. BC and Fe concentrations are substantially higher at
elevations < 6000 m due to post-depositional processes including
melt and sublimation and greater loading in the lower troposphere. Because
the largest areal extent of snow and ice resides at elevations < 6000 m,
the higher BC and dust concentrations at these elevations can reduce
the snow and glacier albedo over large areas, accelerating melt, affecting
glacier mass balance and water resources, and contributing to a positive
climate forcing. Radiative transfer modeling constrained by measurements at
5400 m at Mera La indicates that BC concentrations in the winter–spring
snow/ice horizons are sufficient to reduce albedo by 6–10% relative to
clean snow, corresponding to localized instantaneous radiative forcings of
75–120 W m−2. The other bulk impurity concentrations, when treated
separately as dust, reduce albedo by 40–42% relative to clean snow and
give localized instantaneous radiative forcings of 488 to 525 W m−2.
Adding the BC absorption to the other impurities results in additional
radiative forcings of 3 W m−2. The BC and Fe concentrations were used
to further examine relative absorption of BC and dust. When dust
concentrations are high, dust dominates absorption, snow albedo reduction,
and radiative forcing, and the impact of BC may be negligible, confirming
the radiative transfer modeling. When impurity concentrations are low, the
absorption by BC and dust may be comparable; however, due to the low impurity
concentrations, albedo reductions are small. While these results suggest that
the snow albedo and radiative forcing effect of dust is considerably greater
than BC, there are several sources of uncertainty. Further observational
studies are needed to address the contribution of BC, dust, and colored
organics to albedo reductions and snow and ice melt, and to characterize the
time variation of radiative forcing. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|